The invention provides a solid state display particularly useful as an alternative to LCDs (liquid crystal displays) and LEDs (light emitting diodes), as well as having numerous other applications. As a display, the invention overcomes problems of lifetime, temperature range limitations, and other constraints of prior displays.
The present invention provides a normally transparent semiconductor which is made opaque by removing carriers from the otherwise saturated conduction band. This enables further absorption of incident light in the semiconductor by raising additional carriers to the conduction band. The semiconductor becomes opaque because it can absorb the incident photons. In the disclosed embodiment, means are provided for completing an electric circuit for removing carriers from the conduction band. When the circuit is switched off or open, exiting carrier flow is stopped and the conduction band saturates. This saturated condition prevents further absorption of incident photons, whereby light passes through the semiconductor.
The raising of carriers to the conduction band for changing the refractive index of a semiconductor is known, "The Optical Computer", Abraham et al, Scientific American, February, 1983, pages 85-93, especially page 92. A constant intensity incident beam shines on the semiconductor and is absorbed, page 90, second figure. An additional probe beam causes saturation of the conduction band, resulting in sharply increased transmitted intensity of the beam through the semiconductor, i.e. from an off or opaque condition to an on or transparent condition. Removal of the additional optical probe beam returns the semiconductor to its off or opaque condition. This optical switch is proposed as the building block for a computer based on beams of light rather than electric currents. The optical switch is called a transphasor, and is referred to as the optical analog of the transistor, with the optical probe beam being the triggering or base drive for the transistor.